It is well known to manufacture wood products such as beams or boards out of chips instead out of massive wood. Apart from the known chip-boards, there exist similar types of products made out of so-called "strands" also known in the art as "wafers" or "flakes". These terms as a whole shall mean wood chips having relatively large dimensions, as compared with wood chips which are, for example, produced during the chipping of lateral areas of logs, of barked sections or the like. Typically, a strand has a length of between 200 and 350 mm in the fiber direction, and a width and a thickness in a direction transverse to the fiber direction of between 1 and 15 mm. Wood products such as boards or beams manufactured from such strands by combining and glueing them together are known as "composite beams", "strand boards" or "structural lumber products".
For this purpose, it is also known how to fashion strands with defined width, length and thickness and in certain circumstances with defined chamfered edges so that the strands may be glued in a definite alignment to form planks and beams.
DE 38 37 200 C1 mentioned at the outset discloses a wood chipping machine for the fabrication of such flat chips or strands. This prior art machine is intended to produce large area flat chips having a predetermined thickness, width and length. For that purpose round woods are fed to a chipping drum in a direction perpendicular to their longitudinal extension. The chipping drum comprises an outer cutting rotor together with an inner hammer rotor arranged concentrically thereto. The two rotors are driven in opposite directions of rotation. The cutting rotor cuts chips from the broad side of the round woods which then reach the interior of the drum for being cut into the required flat chips of predetermined dimensions by means of the hammer rotor. The strands thus generated are deflected out of the interior of the chipping drum by means of a baffle and are guided onto a conveyor belt.
In this prior art machine the diameter of the chipping drum is about 60 cm. The prior art machine handles relatively small round woods having a diameter of about 15 cm, i.e. handles trimmed branch pieces and the like. The round wood is thereby entirely chipped.
A method for the fabrication of long strands is disclosed in U.S. Pat. No. 4,371,020 and U.S. Pat. No. 421,149. According to this prior art method a round wood is first shifted through a knife arrangement in an axial direction, the knife arrangement having four knives located along diameters of the round wood and being offset with respect to one another by 45.degree.. The round wood is guided axially through this knife arrangement so that the round wood, when having passed the knife arrangement, is dissected into a total of eight segments being sector-shaped in a radial cross sectional view. These segments are then guided through a spaced arrangement of stationary knives so that strands are generated which are axially parallel. These strands, however, have different widths in a radial direction. They are, subsequently, guided through a cutting roller arrangement in which they are dissected into elongate thin strands having a square cross section.
According to this prior art method the round woods are also completely chipped.
A method and an apparatus for the fabrication of strands is disclosed in U.S. Pat. No. 4,681,146. The strands are also fabricated from the round wood already mentioned in that they are fed in a feed station on a slicer-type table with their broad side upfront. By means of an oscillating slicing plate the round woods are chipped into flat chips. The flat chips are then further dissected by means of knife rollers.
Also according to this prior art method the round wood is entirely chipped.
DE 31 14 843 A1 discloses a so-called "profiling method". During the carrying out of a profiling method the entire logs are firstly profiled, i.e. they are machined in an axial direction by means of corner millers and profile chippers. The result of such working is a so-called model. This term is to be understood to mean a wood product having a radial cross sectional shape being configured for the subsequent dissection of the model into planks and beams for an optimum yield of the wood.
According to conventional profiling methods the areas being chipped off or chipped away by means of profile chippers or corner millers are converted into short chips as are conventionally used for producing cellulose or chip-boards.
U.S. Pat. No. 4,149,577 discloses an apparatus enabling to concurrently generate a plurality of elongate slits in a log by means of saw blades.
It is, therefore, an object underlying the invention to improve a method as mentioned at the outset so that the fabrication of strands becomes also possible outside a field of application where only relatively small round woods (branch pieces) are entirely chipped.